Hybrid diesel electric vehicles, such as hybrid diesel electric locomotives, for example, include an energy storage system with several energy storage devices (i.e. batteries). These energy storage devices are typically utilized to store secondary electric energy during a dynamic braking mode, when the traction motors generate excess electrical energy which may be stored, or during a motoring mode, when the locomotive engine produces excess electrical energy which may be stored. Each locomotive typically includes several energy storage devices, such as between ten and fifty, for example, where each energy storage device is a large massive body including several hundred individual cells combined together, and each amounting to several hundred pounds in weight.
Some of the high temperature storage devices need to be heated to achieve a desired operating temperature. During normal operation of the locomotive, a voltage is typically applied across the heater terminals of each energy storage device, thereby activating an electrical heating circuit to heat the energy storage device. Although each energy storage device is manufactured to operate with consistent operating characteristics under similar operating conditions, the energy storage devices actually operate with varying operating characteristics, when subjected to the same operating conditions. For example, during operation of the locomotive, a maximum temperature storage device operates at a maximum temperature and a minimum temperature storage device operates at a minimum temperature, as compared to the other energy storages devices of the energy storage system. FIG. 13 illustrates an exemplary timing diagram of a maximum temperature 504 and minimum temperature 502 for a respective maximum temperature storage device and minimum temperature storage device of a conventional energy storage system. All other storage device temperatures typically fall within the maximum and minimum temperature of the respective maximum and minimum temperature storage devices. At different times, different energy storage devices may be the maximum temperature storage device with the maximum temperature. Similarly, at different times, different energy storage devices may be the minimum temperature storage device with the minimum temperature. In the illustrated diagram, the time rate of change of the maximum temperature 504 and minimum temperature 502 typically share the same sign at any time instant (i.e. rise and fall together) since they are operated similarly. Additionally, the conventional cooling system for the energy storage system activates when the maximum temperature 504 exceeds a maximum temperature threshold 506, which is approximately 335 degrees Celsius in the illustrated diagram. Further, the conventional cooling system for the energy storage system deactivates when the minimum temperature 502 falls below a minimum temperature threshold 508, which is approximately 270 degrees Celsius in the illustrated diagram. The illustrated diagram in FIG. 13, and particular values are merely an example of a conventional cooling system for a conventional energy storage system, and other systems may operate at varying temperature ranges. Since the operating range of the cooling system, measured by the difference between the maximum temperature threshold 506 and the minimum temperature threshold 508, is greater than the difference between the maximum temperature 504 and the minimum temperature 502, the cooling system can clearly determine whether or not to activate or deactivate at any instant. However, if the difference between the maximum temperature 504 and the minimum temperature 502 exceeded the operating range of the cooling system, the maximum temperature 504 may exceed the maximum temperature threshold 506 while the minimum temperature 502 simultaneously fell below the minimum temperature threshold 508, resulting in confusion as to whether or not to activate or deactivate the cooling system.
Accordingly, it would be advantageous to provide a cooling system for the energy storage devices of a locomotive which reduces the confusion in determining whether to activate or deactivate the cooling system.